Among the means for raising the natality of animals and the viability of their fetuses, the following hormonal preparations are known to be most effective: pregnant mare serum (PMS), super-mutagen (1-4 bisdiazocetyl butane), progesterone, prostaglandins and vitamins.
The use of PMS in sows raises fertility by 1 to 2 piglets, but reduces weight and raises peritoneal mortality of piglets by more than 12%.
The use of super-mutagen for stimulating fertility in mink raises natality up to 7 cubs, as against 6 in the controls.
Progesterone and other hormonal preparations raise the conception rate in sheep by 90 to 96%. Yet, the high cost of hormonal preparations and the complexity of their manufacture reduce their worth very much, hindering their wide-scale introduction into animal breeding practice. In this connection, the US Animal Breeding Association has no plans for introducing hormonal preparations and prostaglandins to raise estrus synchronization in animals.
Trials carried out in Great Britain to check-up sheep fertility assessment methods showed hormonal stimulation to increase the fall of lambs, but this is accompanied by a reduction of their weight, while peritoneal mortality reaches 80 to 85%.